With incentives like that, it's no wonder that athletes will turn to any tools that might help.

However, it wasn't until the mid-19th century and the advent of modern medicine that performance-enhancing drugs really began to take off.

Poisonous Concoctions

From sugar cubes dipped in ether, mixtures of brandy and cocaine, caffeine, cordials containing alcohol, and even nitroglycerine and strychnine, coaches around the world tried to concoct a winning formula to ensure their athlete was first across the finish line.

By the 1930s amphetamines were the pill of choice, helping athletes, soldiers, and college students increase their stamina and alertness.

"It wasn't considered cheating back then," said Ivan Waddington, visiting professor at the Norwegian School of Sports Sciences in Oslo.

Soon after, steroids—drugs derived from hormones such as testosterone—arrived on the scene.

A favorite of bodybuilders, these drugs enable training at increased intensity and reduce the recovery time required between training sessions. Their hallmark is to give users the heavily muscled "Arnold Schwarzenegger" look.

For endurance athletes a favored technique was blood doping—injecting more blood into the body to increase hemoglobin levels, which raises oxygen-carrying capacity to the muscles.

In recent years, a more sophisticated form of this technique involves taking a hormone known as erythropoietin—normally used for treating anemia—to cause more red cell growth.

Unlike some of the early potions and lotions, these 20th-century treatments give athletes a significant edge, but they also tend to carry huge health risks.

Drug-Fueled Tragedy

In 1967 British cyclist Tom Simpson collapsed and died during the Tour de France.

"His autopsy showed high levels of methamphetamine, and a vial of the drug was found in his pocket at the time of his death," Penn State's Yesalis said.

Simpson's death marked a turning point, and by the end of 1967 the International Olympic Committee and member federations began to establish doping-control programs.

"There was a moral panic about drug use in society," Waddington said.

Now every athlete is aware of the extreme damage that performance-enhancers can have.

Steroids, for example, can raise blood pressure, alter the structure of the heart, and cause liver damage in high doses. And erythropoietin can pump blood cell levels so high the blood turns viscous and strains the heart.

But this doesn't seem to deter people from using them.

"Their use is endemic in sport," said Michael Rennie, a clinical physiologist at the University of Nottingham in the United Kingdom.

Outwitting the Testers

With rewards for elite athletes so lucrative, it's unlikely a change in tactics will come anytime soon.

So for drug-testing agencies it's a constant battle to try and keep abreast of the latest developments.

"There are designer drugs out there about which the testers are not aware," Yesalis said, referring to drugs with modified molecular structures that can evade existing tests.

Eventually it may even be possible for athletes to inject genes to enhance their performance.

But for many high-level athletes the benefits associated with performance enhancers outweigh the risks, Waddington believes.

"Health scares are the last thing an athlete is going to worry about," he said. "Elite-level sport by definition is bad for your health."

What's more, clever athletes can minimize their chances of being caught. Steroids, for example, can be flushed out of the body long before a big event.

"By taking steroids in the off-season an athlete can build up their muscle mass," Rennie explained.

As long as they stop taking the drugs far enough in advance the evidence for drug taking disappears, but the stronger muscles remain.

Ongoing investigations may—or may not—reveal whether Bonds and others used such drugs to slug more runs, even as they grow older.

"I'm highly suspicious of his performance, as I am of many other sportspeople," Yesalis said.

But a bigger question, he added, is—if so many of his opponents are using performance-enhancing drugs too—does it really matter?